Many tables, in particular writing desks with table-tops on which the height of the table-top can be adjusted by means of a special drive are available on the market nowadays. The height or inclination of beds such as recliner beds or hospital beds may also be adjusted by means of electrical drives.
It is possible to use DC motors for the drive, operating from a low voltage of about 12 V up to 24 V. For this purpose the main voltage, which in Europe is typically around 230 V, is reduced by a transformer to the lower voltage range of the DC motors, and converted to a DC voltage by a rectifier circuit. The motors can be driven through controlled connection of the motors to the low DC voltage. A controller circuit board, coupled to operating elements, may be used for this and may, for instance, be arranged together with a transformer and the rectifier circuit. It is, however, necessary for this kind of controller to incorporate one or more transformers which, due to the high power consumption of the electric motors, have correspondingly large dimensions and therefore represent a not insignificant cost factor in the manufacture of controllers of this type.
Another option for the drive of electrically adjustable furniture consists in the use of AC motors that can be powered from the alternating main voltage. Here, the AC motors are not regulated, and are simply connected to their supply voltage from the alternating main. In this case, however, the option of regulating the drive is not available. This is particularly problematic if a number of motors need to be operated at the same time and must therefore be synchronized.